Musical instrument switch device



Feb. 14, 1967 J. s. ADAMS MUSICAL INSTRUMENT SWITCH DEVICE Filed May 25, 1964 Hormus United States Patent O 3,304,491 MUSICAL INSTRUMENT SWITCH DEVICE James S. Adams, Fort Wayne, Ind., assignor to The Magnavox Company, Fort Wayne, Ind., a corporation of Delaware Filed May 25, 1964, Ser. No. 369,927 7 Claims. (Cl. 323-95) This invention relates generally to electrical switching systems and more particularly to an electrical switching system particularly adapted for use in electronic organs and similar electrically operated musical instruments.

In a pipe organ the amplitude of sound emitted from the organ increases rather gradually as the air is admitted to a given pipe. In contrast to this, the sound emitted from many types of electronic organs increases to maximum amplitude substantially instantaneously when a key is operated. This produces the effect commonly known as key thump whereby there is more of a percussive eiect than ya gradual attack because of the transient voltage generated when the key-operated switch is closed.

Conventional electronic organs include various types of complex electronic circuits designed to prevent key thump and cause the sound output of the instrument to simulate the sound of a pipe organ. Such circuits add substantial cost and vare not too successful.

The principal object of this invention is to provide a key-operated switch system for electronic organs and similar electrically operated musical instruments wherein transient effects are suppressed or damped when a key is operated and the rate of attack is controlled to produce sound simulating that of a pipe organ.

Another object of this invention is to provide, in electronic musical instruments, a simple and inexpensive control circuit for damping transient effects in key-operated circuits.

In accordance with this invention there is provided a key-operated switch and circuit comprising an elongated flexible conductor operable by a key and connected to a source of sound signals, a first contact normally closed with said conductor and comprising a compressible conductive material providing a relatively high impedance to ground, a second contact comprising conductive compressible material connected to an output circuit and normally spaced from said flexible conductor, said ilexible conductor being operable to initially compress said first contact to increase current to ground and subsequently operable to engage said second contact, compressing it to gradually increase signal output therethrough while disengaging from said first Contact.

The full nature of the invention will be understood from the accompanying drawings and the following description and claims.

FIG. l isa side elevation partially in section of a switch arrangement embodying the present invention.

FIG. 2 is a schematic View illustrating the principle of operation of the switch arrangement of FIG. l.

FIG. 3 is a graph showing output current or voltage plotted against time for the switch arrangement of the present invention.

Referring now more particularly to the drawings, there is illustrated a switch structure which in one embodiment might include a frame 11 made up of a plurality of members 12, 15 and 16 fixed relative to one another. The member 15 in the present embodiment is electrically nonconductive. The frame 10 further includes a member 17 having an aperture 18 through which extends a lever 20. The lever 20 may be an organ key or con- .nected thereto and forms part of a mechanical linkage 2l by means of which the switch structure is actuated.

3,334,491 Patented Feb. 14, 1967 ice The lever 20 is pivotally mounted to the frame member 18 so that the end 22 of the lever is movable between the solid line position of FIG. l and the dotted line position of FIG. l. The end 22 of the lever projects through an aperture in an elongated actuator 25 for operating it between the solid and dotted line positions. The elongated actuator 25 is formed of insulating material such as, for example, polyethylene and has a plurality of apertures 30 therethrough which slidably receive the free ends of conductive spring contact elements 31.

Each of the spring contacts 31 is `formed at its proximal end 32 in the shape of a hook with a portion 35 extending inwardly toward the main body of the member 31 whereby the member 31 can be removably secured in electrically nonconductive relation to the member 15. Each member 31 extends through a pair of spaced apertures 36 and 37 in the member 15 and is thereby secured thereto.

A plurality of insulating members 4t) are stacked between the members 12 and 16 and support, in turn, insulating members 41 which, in turn, fixedly support electrical buses 42 and 43. Mounted within each of the electrical buses 42 and 43 are laterally spaced electrical contacts 45 and 46 which are formed of conductive resiliently compressible material having a conductance which increases as the compressive deformation of the respective contact increases and which decreases as the compressive deformation of the contact decreases. This material might be, for example, any conventional commercially available resilient plastic or polymer such as vinyl, silicone rubber, buna rubber or any other material having the desired conductive characteristics.

For purposes of convenience in the description which follows, only a single switch circuit, for example, will be described. When the associated organ key is not depressed, the lever 2li is in the solid 4line position of FIG. 1 as are the actuator 25 and the spring contact 31. The contact 31 has -a certain amount of resiliency or rigidity which causes it to bear against the contact 45 with a certain amount of pressure. As is indicated in schematic FIG. 2, the contact 45 is connected to ground 51 through the low impedance of the compressively deformed contact 45 as represented by impedance 52, said impedance 52 being low as compared to the output load (not shown).

The contact 46 forms the output contact for the switch while input conductors 34 may be connected to the end portions 35 of spring contacts 31. When the lever 2t) iS moved from the solid to the dotted line position, the switch moves from fully open to fully closed condition. This movement takes a nite period of time which is indicated in the graph of FIG. 3 as being the time on the horizontal axis between the numeral #1 and the numeral #3.

The output voltage or current desired and obtained from the present -device is indicated by the curve 55 which slopes -from the time `point #l at a relatively high rate and iiattens centrally at 55 or time point #2, then has an increasing slo-pe until it reaches full current at 57 or -time point #3. This desired output characteristic is effected by the movement of the actuator from the illus- Itr-ated solid line position to the dotted line position.

In position #1, the movable contact 31 engages the ground contact 45 with -a predetermined pressure grounding the input through the normally -low isolating impedance created when contact 45 is under pressure, thereby reducing the signal present on the movable contact. As the movable contact is `transfer-red to position #2, the reduced signal is impressed upon the xed output oontact 46 through the relatively high resistance oered by the relatively low pressure `between the Contact 31 and the contact 46. As 4the contact 31 is further moved toward position #3 the resistance in series decreases due to the increased pressure on the fixed output contact 46. Further movement of c-ontact 31 toward position #3 increases the resistance to ground through contac-t 45 because the pressure between contact 45 and con-tact 31 is reduced. Still further movement of contact 31 toward position #3 separates contact 31 from contact 45, and pressure between contact 31 and contact 46 reaches a maximum, thereby to provide a low series resistance between the movable contact 31 and the fixed contact 46. The above described action of contacts 31, 45 and 46 produces the output curve illustrated in FIG. 3 whereby transient voltages are damped and a gradual attack is produced, thereby to prevent key thump.

It should be understood that various Ialternative embodiments ofthe Ipresent invention are possible. For example, the output contact 46 might be located between the `grounded contact 45 and the support member 15. In this embodiment, the actuator would act against the contact 31 at a point between the Ioutput contac-t 45 and the input end of contact 31. Similarly to the above described embodiment, this embodiment would vhave an initial nonact-uating position wherein the contact 51 engages the contact 45 and a final fully actuated position in which the contact 31 has moved 4away from the contact 45 and is fully engaged with the contact 46.

It should be pointed out that the speed lof closure of the contacts 31 and 46 is less than the speed of the actuator 25 because of the fulcrum action involved in the initial engagement -of the contact 45 by the 'contact 31. This reduced closure rate also cooperates to reduce the rate lof the change lof resistance of the contact 46 slowing down or damping the on transient.

Various other modifications `of the specific structure 4of the invention lare possible. For example, the movable contact 31 might be a flexible wire conductor of any cross sectional shape land may or may not be plated or clad with precious metal. Preferably means are provided lfor opening or restoring the switch, that is, for moving the actuator back from its dotted line to its solid line position. Such means lmight include gravity or a suitable sprin-g or springs. The operation of the switch is actually reversed when so opened. That is, the current or voltage output moves along the same curve as illustrated in FIG. 2 but from right to left.

While the invention has been illustra-ted and described in detail in the drawings and yforegoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiment has been shown and described and that all changes and modifications that come within the spirit of Ythe invention and the scope of the claims are also desired to be protected.

The invention claimed is:

1. A switching system comprising an input terminal, an elongated flexible contact member fixed at one end thereof to said terminal, a pair of spaced contacts aligned with said member intermediate its ends, means connect- .ing one of said contacts to ground, an actuator coupled to the other end of said member and normally positionedV Y :to engage said member with said one contact, and means :for moving said actuator and therewith the said other lend of said member to flex said member, first into simultaneous engagement with both of said contacts, and then :into engagement solely with the other of said contacts, said contacts being formed of conductive deformable material having a conductance varying with pressure thereon.

2. A switching system comprising an input terminal, an elongated flexible Contact member flxedy at one end thereof toV said terminal, a pair of spaced contacts aligned with said member intermediate its ends, means connecting one of said contacts to ground, an actuator coupled to the other end of said member and normally positioned to engage said member with said one contact with predetermined pressure to provide predetermined current ow to ground, and .11K-2.11.15 for moving said actuator and therewith the said other end of said member to flex said member, first into simultaneous engagement with both of said contacts, and then into final engagement solely with the other of said contacts, said contacts being formed of conductive deformable material having a conductance varying with pressure thereon, said one ground connected contact and said member comprising a means for gradually increasing the voltage at said other contact as said actuator moves said member from its normal position to its nal engagement with said other contact. Y

3. A switch arrangement comprising an input terminal, an output contact formed of conductive resiliently compressible material having a conductance varying directly as the compressive deformation of the output contact, a further contact f-ormed of conductive resiliently compressible material having a conductance varying directly as the compressive deformation of the further contact, a flexible conductor electrically connected to said terminal and engaging said further contact, means for actuating said flexible conductor to move it into engagement with said output contact and out of engagement with said further contact. t

4. A switching system comprising an input terminal, an output contact formed of conductive resiliently compressible material having a conductance varying directly as the compressive deformation of the output contact, a further contact connected to ground, said fulther contact being positioned adjacent said output contact and being formed of conductive resiliently compressible material having a conductance varying directly as the compressive deformation of the further contact, an elongated flexible conductor electrically connected to said terminal and engaging said further contact with sufficient pressure to provide a low impedance to ground, and means for actuating said flexible conductor to move it into engagement with said output contact and out of engagement with said further contact.

5. A switch comprising a frame, a conductive element secured at one end to said frame, an actuator reciprocably mounted on said frame and coupled to said element, a pair of electrical contacts mounted in spaced relation on said frame in the path of movement of said element, said contacts being formed of conductive resiliently compressible material having conductances which increases as the compressive deformation of the respective contact increases and which decrease as the compressive deformation of the respective contact decreases, said actuator being movable between a first position in which said element forcibly engages one of said contacts and Vnot the other and a second position in which said element forcibly engages the other of said contacts and not the one, said actuator when moving between said rst and second positions also moving through an intermediate position wherein said element engages both of said contacts with a lesser force.

6. A switching system comprising a frame including a conductive terminal, an elongated spring element secured at one end to said terminal, an actuator connected to said Vspring element and reciprocably mounted for longitudinal movement on said frame, a pair of electrical contacts mounted in spaced relationon said frame, and in the plane of movement of said spring element, said contacts being formed of conductive resiliently compressibleV material having conductances which increase as the compressive deformation of the respective contact increases and which decrease as the compressive deformation of the respective contact decreases, said actuator being movable between a rst position in which said spring element forcibly engages one of vsaid contacts and not the other and a second position in which said spring element forcibly engages the other of said contacts and not the one, said actuator when movi-ng between said first and second positions also moving through an intermediate position wherein said spring element engages both of said contacts with a lesser force.

7. A switching system comprising a frame including a conductive terminal, an elongated spring element secured at one end to said terminal, an actuator formed of insulating material and reciprocably mounted for longitudinal movement on said frame, said actuator having an aperture therein through which the other end of said spring element projects, a pair of electrical contacts mounted in spaced relation on said frame, said contacts being formed of conductive resiliently compressible material having conductances which increase as the compressive deformation of the respective contact increases and which decrease as the compressive deformation of the respective contact decreases, said actuator being movable between a first position in which said spring element forcibly engages one of said contacts and not the other and a second -position in which said spring element forcibly engages the other of said contacts and not the one, said actuator when moving between said first and second positions also moving through an intermediate position wherein said spring element engages both of said contacts with a lesser force, said other contact being connected to the output load', said one contact being connected to ground to provide impedance to ground which is low compared to said output load when said actuator is in said rst position.

References Cited by the Examiner UNITED STATES PATENTS 2,959,693 l1/l960 Meyer ZOO-166.1 3,060,784 10/1962 Holt 20G-166.1 3,125,737 3/1964 McKee et al. 338-69 3,206,701 9/1965 Gregory 338-69 JOHN F. COUCH, Primary Examiner. A. D. PELLINEN, Assistant Examiner. 

3. A SWITCH ARRANGEMENT COMPRISING AN INPUT TERMINAL, AN OUTPUT CONTACT FORMED OF CONDUCTIVE RESILIENTLY COMPRESSIBLE MATERIAL HAVING A CONDUCTANCE VARYING DIRECTLY AS THE COMPRESSIVE DEFORMATION OF THE OUTPUT CONTACT, A FURTHER CONTACT FORMED OF CONDUCTIVE RESILIENTLY COMPRESSIBLE MATERIAL HAVING A CONDUCTANCE VARYING DIRECTLY AS THE COMPRESSIVE DEFORMATION OF THE FURTHER CONTACT, A FLEXIBLE CONDUCTOR ELECTRICALLY CONNECTED TO SAID TERMINAL AND ENGAGING SAID FURTHER CONTACT, MEANS FOR ACTUATING SAID FLEXIBLE CONDUCTOR TO MOVE IT INTO ENGAGEMENT WITH SAID OUTPUT CONTACT AND OUT OF ENGAGEMENT WITH SAID FURTHER CONTACT. 